Retreating Antarctic Ice Fuels Surprising Glass Sponge Invasion

A fish (Trematomus sp.) is hiding in a glass sponge. Photo taken at the study site in the Western Weddell Sea. Photo: Thomas Lundalv, Alfred-Wegener-Institut

In the frigid, inky ocean depths beneath permanent ice shelves, life tends to move pretty slowly. But a recent expedition to the seafloor under a newly thawed Antarctic ice sheet has revealed an unexpected invertebrate invasion. Some of Earth’s strangest species, a group of ghostly pale sponges made of glass, have set up shop there in a hurry, upending much of what scientists know about these exotic creatures.

Thanks to changes in this ecosystem brought on by a warming climate, these gardens of glass sponges have sprouted up in only a few years, a veritable population explosion for species once thought to take decades or centuries to spread. It suggests that glass sponges could find themselves squarely on the winner’s podium when it comes to climate change.

In 2011, a team led by researchers from the Alfred Wegener Institute for Polar and Marine Research completed a new census of glass sponge growth on the seafloor underneath the Larsen Ice Shelf in Antarctica’s Weddell Sea, following up on a similar survey done in 2007. Their surprising results were published today in Current Biology.

Glass sponges like those found in the western Weddell Sea are not well studied because they live in deep water beneath polar ice sheets. Ironically, surveys in this area are only possible today because two-thirds of the Larsen Ice Shelf no longer exists, disintegrating without warning in 1995 and 2002. Navigating the German research icebreaking vessel Polarstern through the icy waters there, the team was able to carefully pilot their remotely operated vehicle (ROV) along the same path studied in 2007. Their cameras got an unprecedented view of the same seafloor at two different points in time (video below).

To their surprise, large numbers of glass sponges had taken up residence on the seafloor in just a few years. Occasional observations had suggested that glass sponges are capable of short growth spurts, but the consensus held that these species multiplied on the timescales of redwoods, not weeds. This new research provides the strongest evidence yet that glass sponges are capable of rapidly reproducing and colonizing large areas of seafloor in short amounts of time, although the reasons why remain uncertain.

Claudio Richter, an author of the new study, has one theory. He thinks the thawing of the Larsen ice shelves has created a veritable feast in this extreme environment. The newly exposed ocean exposed a fresh habitat for sun-loving phytoplankton near the surface. Although these blooms are small and sporadic compared to those seen elsewhere, Richter explains that a rain of algae and phytoplankton can reach all the way down to the seabed 300 meters below the surface, where glass sponges are bathed in complete darkness. More plankton alone is not enough to explain the accelerated growth, though. These deep water residents are picky eaters.

Marine ecologist Paul Dayton, who was not involved in the study, spent decades studying glass sponges at the Scripps Institute of Oceanography. He says they depend primarily on only the smallest species of plankton and aquatic microbes for food. With the ice shelf gone, Dayton speculates that bacteria were swept up from the ocean floor, providing a boost in the specific prey the sponges required.

Glass sponges are one of the oldest examples of complex life that survive today. These long-living, cold-water invertebrates trace their evolutionary history back more than 550 million years, predating the so-called Cambrian explosion when most of today’s animal lineages originated. Today, most of the complex species alive in pre-Cambrian times exist only as fossils, yet somehow this family of ancient ocean-dwellers lives on in the flesh. The oxymoronic glass sponge gets its name from the surprising material they use to build their skeletons. Instead of the calcium-based structures that support organisms like coral and vertebrates, glass sponges extract silicon from sea water to erect elegant glass lattices, able to withstand the crushing pressures present hundreds of meters below the surface.

Glass sponges like Rossella cf. villosa provide habitat and 3-D structure for other Antarctic benthic organisms, for instance for feather stars (on top of the sponge) and brittle stars (attached to the sponge). Photo from the study site in the Western Weddell Sea. Photo: Thomas Lundalv

Like tropical corals, the nooks and crannies of glass sponges provide important habitats for other sea creatures like fish and feather stars. Reaching heights of up to 2 meters, glass sponges add a third dimension to an otherwise flat seafloor.

But Richter says not all of the sponges’ new neighbors may be friendly, and while so far the sponges seem to be taking advantage, the ultimate fate of this peaceful invasion remains to be seen. “We don’t know if this success will go on,” he said, “or if predators catch up diminishing their numbers in the next couple of years. Or possibly competitors show up. There are many unknowns making predictions very difficult.”

Whether these new residents’ ultimate impact on the rich Antarctic ecosystem will be good or bad — or neither — is impossible to predict. “It is what it is,” Dayton said. “I don’t see nature as good or bad, although it is very bad to have a human-caused phenomenon result in huge changes.”

Richter, meanwhile, is more excited about the new questions presented by this work rather than what it says about climate change.

“It is indeed an awesome experience to work in previously uncharted waters in one of the most inaccessible places on the planet,” Richter said. “There is so much to discover. Every day is likely to yield unexpected insights into this magnificent ecosystem.”

Dayton agrees. “This sort of experience is what make science so much fun for all of us. Nature just has so many wonderful surprises.”

Here’s The Thing With Ad Blockers

We get it: Ads aren’t what you’re here for. But ads help us keep the lights on. So, add us to your ad blocker’s whitelist or pay $1 per week for an ad-free version of WIRED. Either way, you are supporting our journalism. We’d really appreciate it.